1. Field of the Invention
The present invention generally relates to a sensor having selective binding affinity for an analyte which is indicative of, for example, food spoilage.
2. Description of the Related Art
Food spoilage such as meat and fish spoilage occurs as bacteria begin to grow unchecked following respiration and circulation cessation at the time of slaughter. One of the markers of meat spoilage is the decarboxylation of free amino acids on and in the meat by enzymes released by spoilage microorganisms. Two of these products, putrescine and cadaverine, are particularly distinctive in odor, correlate well with surface bacterial counts, and are widely used to evaluate meat freshness both by trained meat inspectors and the individual consumers. Another product, histamine, is of interest due to its apparent ability to potentiate histamine intoxication, a form of food poisoning associated with the consumption of spoiled fish.
To detect the occurance of meat spoilage, sensors, e.g., polymeric sensors, have been developed. Polymeric sensors are typically prepared by ionically or covalently attaching an atomic, ionic, or molecular site to a polymer that, upon association with a particular analyte, will exhibit a detectable change in a measurable physical property. Exemplary measurable physical properties include spectroscopic (i.e., electronic absorbance or luminescence), electrochemical, or magnetic properties. The change in the physical property then provides a probe for the presence or absence of the associated analyte that can be measured using appropriate instrumentation or by direct observation. The polymer provides a support matrix that serves to immobilize the sensor sites and provide a localized density of the sensor sites as a means of optimizing detection of the analyte.
Molecular imprinting essentially involves making a polymer cast of a target molecule. The process of making the polymer cast involves dissolving the target molecule to be imprinted in a suitable solvent. Normally, a co-monomer, cross-linking monomer and a polymerization initiator are added to the reaction mixture. Radiation (photochemical or ionizing), thermal energy, or a chemical initiator is then applied to the reaction mixture to drive the polymerization process, ultimately resulting in the formation of a solid polymer. The resulting polymer may be processed using conventional polymer processing technologies, assuming those processes do not alter the structure of the molecularly imprinted sites. The imprinted molecule is extracted using methods appropriate for dissociating the target molecule from the polymer. Details of target molecule dissociation from the polymer are dependent upon the nature of the chemical interaction between the target molecule and the polymer binding site. The polymer dissociated from the target molecule possesses binding sites optimized for the structural and electronic properties of the target molecule. U.S. Pat. No. 5,110,833 describes the preparation of synthetic enzymes and synthetic antibodies by molecular imprinting techniques.
U.S. Pat. No. 6,593,142 discloses a polymeric food spoilage sensor wherein a polyazamacrocyclic transition metal complex selectively binds biogenic amines, such as cadaverine, putrescine and histamine, which are released by food spoilage microorganisms. The polymer then undergoes a detectable color change upon exposure to the biogenic amine, thus indicating that food spoilage has probably occurred. However, the polyazamacrocyclic transition metal complexes react slowly with cadaverine such that it can take several hours before a noticeable color change will occur.
Accordingly, there is a need for a sensor which accurately, simply and rapidly detects the presence of biogenic amines in fluids such as food products and body fluids.